The present invention generally relates to apparatuses for supplying fluid of preset quantity, and more particularly to an apparatus capable of accurately supplying fluid of preset quantity without introducing oversupply of fluid.
Conventionally, in most general apparatuses for supplying fluid of predetermined quantity, an accumulated flow quantity value measured by a flowmeter is supplied to a preset counter, and the preset counter generates a control signal when the accumulated flow quantity value coincides with a preset value of the preset counter, to close a valve by the control signal. However, the quantity of fluid which flows from the time the valve begins to close and the time the valve actually closes completely, should not be supplied. This quantity of fluid which actually should not be supplied, is the so-called oversupply quantity.
Accordingly, there are apparatuses which use a two-step valve closing system in closing the valve, in order to reduce the above oversupply quantity of fluid. In these apparatuses, the valve which is in a fully open state is closed by a certain amount when the supplied quantity of fluid reaches a value close to a predetermined quantity to continue the supply of fluid with a small flow quantity, and the partly closed valve is closed completely when the supplied quantity of fluid reaches the predetermined quantity, so as to improve the accuracy of the apparatus. However, a valve driving device having a complex construction is required to close the valve in two steps as described above. Therefore, the construction of the fluid supplying apparatus as a whole became complex. Moreover, even when the valve is closed in the above two steps, the oversupply quantity of fluid cannot be completely eliminated, and there was a limit in improving the accuracy of the fluid supplying apparatus.